Wound healing implants should have the ability to adhere and conform to the wound site, and ideally should facilitate regrowth of epidermis, and accumulation of fibroblasts, endothelial cells, and wound healing regulatory cells into the wound site to speed healing (e.g., promotion of connective tissue deposition and angiogenesis). Whether a given implant can meet these objectives is a reflection of the chemical composition and physical characteristics of the implant.
Collagen, the major protein of connective tissue, has been used previously in wound dressings. Procedures for rendering xenogeneic collagen substantially nonimmunogenic are available. U.S. Pat. No. 4,412,947 describes an absorbent dressing having a bulk density of 0.005 to 0.0065 g/cm.sup.3 made by freeze drying a dispersion of native collagen in a weak aqueous organic acid solution. Such dressings that are made from acid solution have tightly woven fibers with typically low absorptive capacity and pore sizes that do not encourage optimum cell ingrowth.
PCT application no. 85/04413 describes a carbodiimide or succinimidyl ester cross-linked collagen sponge formed from a dispersion or solution of collagen that is dehydrated before or after the collagen is cross-linked by addition of the cross-linking agents. Collagen sponges made in this manner have similar disadvantages to those made from the freeze dried acid solution.
Other references describing collagen sponges are U.S. Pat. Nos. 3,742,955, 3,743,295, 3,810,473, 4,515,637, and 4,578,067.
The present invention is directed to providing collagen implants that are biocompatible, biodegradeable, and are capable of promoting connective tissue deposition, angiogenesis, reepithelialization, and fibroplasia. Another aspect of the invention is directed to providing a collagen matrix useful for sustained delivery of bioactive agents.